Interleaved electroacoustical transducer



May 4, 1965 Filed Feb.

C. E. GREEN INTERLEAVED ELEGTROACOUSTICAL TRANSDUCER 2 Sheets-Sheet l lI I l l I 1 ul- /9 4 /6 2/ 0 /7 27 l ,5 i I 18 TRANSCEIVER PHASE SHIFTERI 2 lg. 3 as Fig. 4

INVENTDR.

CHARL 55 E'. GREEN k AZ'T R/VEYS y 4, 1965 c. E. GREEN 3,182,284

INTERLEAVED ELECTROACOUSTICAL TRANSDUCER Filed Feb. 25, 1960 2Sheets-Sheet 2 Fig 5 FREE FIELD VOLTAGE (db) a i O O IN V EN TOR.

Fig 6 CHARLES E. GREEN L ATTO N YS United States Patent 3,182,284INTERLEAVED ELECTRQACOUSTECAL TRANSDUCER Charles E. Green, San Diego,Calif., assignor to the United States of America as represented by theSecretary of the Navy Filed Feb. 25, 1960, Ser. No. 11,113 11 Claims.(Cl. 340-9) (Granted under Title 35, US. Code (1952), see. 266) Theinvention described herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

This invention relates generally to apparatus for radiating andreceiving acoustical energy and in particular concerns a reversibleelectroacoustical transducer for directionally broadcasting andreceiving energy in the acoustical frequency range within an aqueousmedium.

Although it is known to use single piezoelectric elements and arrays ofpiezoelectric elements as acoustical projectors, and that they performthe function of converting electrical energy into acoustical energy andvice versa in a satisfactory manner for many operational purposes, ithas been found to be difiicult to predetermine and con trol thedirectivity and power characteristics thereof without includingelaborate associated supporting structure and perhaps appropriatereflectors and deflectors, etc. The present invention, however, requiresonly relatively simple associated supporting structure and need not beused in conjunction with expensive reflectors and deflectors in order tobroadcast or receive energy patterns having desirable forms and powercharacteristics. The basic idea embodied in the structures constitutingthis invention is exceedingly simple per se, but when properly employedin appropriate structure it becomes profound indeed, inasmuch as itachieves exceptional operational results which are considerableimprovements over the prior art for its intended purposes.

It is, therefore, an object of this invention to provide anelectroacoustical transducer assembly that will produce substantiallypredetermined broadcast and reception radiation characteristics fromnondirectional piezoelectric elements.

A further object of this invention is to provide an electroacousticaltransducer whose relative phase and amplitude characteristics may bevaried essentially as desired.

Another object of this invention is to provide an electroacousticaltransducer operationally characterized by substantially free-fieldresponse patterns.

Another object of this invention is to provide an improved transducerthat will produce a horizontal plane directivity pattern that isproportional to the total length of a plurality of stacked projectorelements when operated in the fundamental mode.

A further object of this invention is to provide an improvedelectroacoustical transducer that cancels sound pressure in accordancewith the direction of offset of a plurality of individual projectingelements.

Another object of this invention is to provide an electro acousticaltransducer that produces a predetermined horizontal bi-directional orunidirectional sound beam within an operating medium.

Another object of this invention is to provide a transducer having sonicbeam widths and beam attenuation characteristics dependent on the offsetdistance between the electroacoustical convertor units and theexcitation frequency applied thereto.

A further object of this invention is to provide a sound projector thatwill efficiently operate in an acoustical spectrum band of at least 0.7octave.

3,l82,284 Patented May 4, 1965 Last but not least, it is an object ofthis invention to provide an improved reversible submarineelectroacoustical transducer that is easily and economically constructedand maintained.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of a representative diagrammatic embodimentof the inventive idea of interleaving the piezoelectric cylinders of twostacks of piezoelectric cylinders with their respective axes parallelbut displaced with respect to each other;

FIG. 2 is an elevational view, partly in section, of the transducerconstituting this invention combined with a phase shifter circuit;

FIG. 3 is an elevational view, partly in section, of another embodimentof the transducer constituting this invention;

FIG. 4 is a schematic diagram of a phase shifter circuit which may beused with the subject transducers;

FIG. 5 is an exemplary graphical illustration of the horizontalradiation patterns that may be obtained from varying the relative phaseof the two vertical projector stacks with signal wavelength and stackoffset distance; and

FIG. 6 is a graphical representation of the free-field voltage responseof the invention that may be obtained under various operationalconditions.

Referring now to the drawing, there is shown in PEG. 1 a first stack ofthin cylindrically shaped piezoelectric convertor elements 121.spacially aligned along a common axis 12. Alternately and partiallyinterleaved between piezoelectric converter elements 11 is a secondstack of thin cylindrical piezoelectric converter elements 13 spaciallydisposed along a common axis 14 which may be otfset a given desireddistance d from axis 12.

The piezoelectric convertor elements disclosed as preferred embodimentsherein are substantially cylindrical in shape with their diametricalplanes essentially parallel; nevertheless, it should be understood thatthe shape and angular relationship therebetween may be varied to containany desired geometrical configuration having any desired centroid offsetdistances without violating the spirit or scope of this invention. Forexample, in some instances, it may be to an advantage to make saidpiezoelectric elements cube in shape or oblong block in shape orirregular block in shape and so doing should be considered to be wellwithin the purview of this disclosure. Likewise, the dimensions andangular relationships of the various disclosed elements of thisinvention may be varied as expedient. However, it has been determinedthat when cylindrical piezoelectric convert-or elements are operated attheir gravest mode, that the diameter thereof should be approximately awavelength across with the offset distance therebetween something lessthan a wavelength in order to establish the desired free-field responsepatterns. Obviously, to accomplish this, the interleaving feature mustbe employed.

Because stacks of individual cylinders are actually interruptedradiators along the axis of the stack, it becomes necessary to minimizethe resulting interrupted radiation effect so that substantiallycontinuous axial radiation will occur. This may be effected by usingshort or thin cylinders so that the axial distance between radiators ofthe same phase is less than one-third wavelength at any given frequency,thereby causing the sum of the individual radiators to appear as acontinuous line.

FIG. 2 illustrates one of the preferred embodiments of the invention asa right hand axially aligned stack of piezoelectric converter elements15 made of, for example,

I with. Each of the right hand convertor elements are respectively indirect contact with or are partially impregnated with upper and lowerelectrodes 17 and 18 mounted to excite same when the subject transduceris being used as a sound projector and also mounted to be excited bysaid convertor elements when said transducer is being employed as anacoustical energy receiver. Likewise and for like purpose, upper andlower electrodes 19 and 20, are respectively mounted on left handconvertor elements 16. Alternate convertor elements and their adjacentlyassociated electrodes are separated by insulators 21. Allconvertor-electrode assemblies or projector units contain an aperture 22normal to the diametrical planes thereof through which extends a hollowelongated insulating pipe 2 3. The entire transducer assembly is heldtogether by a threaded shaft 24 extending through said hollow pipe and apair of nuts 25 and 26 in such manner that each of the piezoelectricconvertor elements and their respectively associated electrodes arephysically and electrically insulated from each other as individualenergy projecting units. I

Completely surrounding each of the projector units is an electricallyinsulating but substantially acoustically clear material 27 which servesto electrically insulate same from the ambient aqueous medium and stillallow passage of sonic pressure waves therethrough. Such material may beof any appropriate resilient types such as rubber or the like, butpreferably'it should have physical characteristics which enable it topass sonic energy with minimum resistance and distortion.

An extension 28 of shaft 24 may be used as a means for fastening theentire transducer to any appropriate support structure such as, forexample, the deck or hull of a ship or submarine boat.

The convertor elements of each stack of projector units are shown ashaving their respective associated electrodes electrically connected inparallel, forming two separate energy projectors which may be excited inany given .phase relationship as operational circumstances warrant,although series connection thereof may be used as well if so desired. Aphase shifter 29, which was inserted by a previous amendment isappropriately coupled through insulated electrical conductors to theparallel connected electrodes of each stack of convertor units for thispurpose. Any appropriate signal source or receiver may be used as theexcitation means for the entire transducer or as a utilization meanstherefor, respectively. Accordingly, a transceiver 51 is optionallyconnected to the aforementioned phase shifter 29 for these purposes.

FIG. 3 depicts another preferred embodiment of the subject invention ashaving a pair of energy projectors and receivers each of which contain astack of converter elements disposed along a common axis, the respectiveconvertor elements of which are interleaved with the other. The stackshave a plurality of right hand and left hand piezoelectric elements 30and 31, respectively. Associated with elements 30 are a plurality ofupper and lower electrodes 32 and 33, and associated with elements 31are 'a plurality of upper and lower electrodes 34 and 35. Of course,these piezoelectric elements and their associated electrodes are alsoelectrically insulated as units from their ambient environment byacoustically clear resilient material 36 such as rubber or the like in amanner similar to the projector units of FIG. 2 mentioned above.Separating the electrodes of adjacent projector units are shelves 37 ofany suitable structural material such as, for example, rubber, metal,wood, plastic, etc. These shelves serve to isolate one projector unitfrom another as well as physically secure all of the projector units ofboth stacks when firmly clamped by a plurality of threaded shafts 38passing through apertures 39 containedin suitable locations in saidshelves and nuts 40. Extensions 41 of shafts 38 may be employed tofasten the entire transducer assembly to any appropriate supportingstructure.

It should be noted that all of the cylindrical projector units need notbe the same size. In particular, the embodiment shown in FIG. 3discloses the end projector units 61 and 62 to be somewhat larger thanthe others. Because the acoustic impedance of the end cylinders isdifferent from the rest, compensation may be made therefor in one or twoways. Change of physical size of the end projector units is one way and,since a different acoustic impedance reflects a different electricalimpedance as well, using a different electrical driver to excite the endpiezoelectric convertors in another Way. In general, where an alignedplurality of identically sized cylinders are used, the end cylindershave a lower acoustic load and, consequently, will resonate at a higherfrequency. To overcome this, the end cylinders of a line should be madelarger in diameter and of the same resistive component to the compleximpedance as the inner cylinders if they are to be driven from the sameelectrical driver. This may also provide the additional benefit that, ifthe transducer is to function at maximum power limited only bycavitation of the medium within which it is operated, the largercylinders on the ends having greater radiating surfaces help compensatefor the lower cavitation threshold of poorly loaded cylinders.

The device of FIG. 3 is also shown as having each individual projectorunit of each stack coupled in parallel with both stacks adapted to beingconnected to effectively separate electrical driving means for excitingeach stack with a phase relationship different from that of the other.Of course, the preferred embodiments disclosed herein employ only twostacks of axially aligned, parallel connected, energy projectors; but,it should be understood that any number of stacks or individual offsetprojector units may be used in conjunction with pertinent support andexcitation and phase shifting means connected thereto without deviatingfrom the scope and spirit of this invention, in event it becomesnecessary to so do in order to obtain desired radiation patterns duringeither broadcast or receiving operations. Likewise, it should be notedthat magnetostrictive elements and appropriate excitation means such asenergized electrical coils or the like may be respectively substitutedfor the piezoelectric projector elements and their excitation meanswithout deviating from the scope and spirit of this invention.

Referring now to FIG. 4, the phase shifter means thereof is illustratedas including a pair of input-output terminals 42 adapted to be connectedto an external power source having electrical conductors leadingtherefrom with a variable resistor 43 and a capacitor 44 seriesconnected thereacross. Also series coupled across said conductors is avariable inductance 45 and capacitor 46. The negative terminal ofinput-output terminals 42 is also the negative terminal of a pluralityof terminals 47 which are adapted to being connected to like terminalsof the transducer assembly through appropriate insulated conductors. Thetwo positive terminals of the aforesaid plurality of terminals 47 areobtained from conductors connected to the junction of variable resistor43 and capacitor 44 and the junction of variable inductance 45 andcapacitor 46, respectively.

Operation of the subject invention is briefly as follows:

When the transducer is being operated as a sound source and acousticalenergy projector within an aqueous medium, electrical driving power isapplied across the electrodes of each projector unit of each stack. Eachof the cylindrical piezoelectric convertors are thereby caused to changesize in proportion to the potential difference applied thereto andproduce an omnidirectional sonic pressure wave which radiates therefrom.As the radiating sonic pressure wave from one stack interferes with thatof the other stack, cancellation thereof occurs, leaving a null area andresulting in a radiation pattern in accordance with the relative phaseof the driving powers applied to the two stacks and the offset distancebetween stacks.

FIG. 5 indicates that control of the radiation pattern is feasible andillustrates some of the various and sundry radiation patterns that maybe obtained by regulating variable resistance 43 and variable inductance45 which, in turn, regulates the relative phase represented by theordinant and the offset represented by the term d/)\ as an abscissa,where d is the distance between axes of the stacks, as measured parallelto said ordinant and is the wavelength of the acoustical signal beingbroadcast.

FIG. 6 shows the free-field voltage response where the offset in thecylinders was adjusted to make the cutofi frequency coincide with theresonant frequency and the relative phase between stacks equal to zero.The upper response curve is that of the main lobe. The lower curve istaken at a 90 horizontal rotation to the main lobe. The interleavedcircles and arrows, of course, show the relative offsets and energyradiation directivity, respectively. This response then, for example,goes through the null as shown at approximately d/)\=.55. The difference between the curves shows the front-to-side ratio in directivity.

When the subject invention is acting as an energy receiving means orhydrophone, the process is essentially reversible as far as radiationpatterns and response thereto are concerned. Of course, the energytransfer is reversed and the piezoelectric elements convert receivedacoustical energy into proportional electrical energy.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise then as specifically described.

What is claimed and desired to be protected by Letters Patent of theUnited States is:

l. A transducer comprising a plurality of stacks of acoustical energyprojectors each of which is successively and alternately interleavedwith the others along a like plurality of respective axes each of whichis spatially disposed from the others, means connected to each of saidacoustical energy projectors for timely electrical excitation thereof,and support means connected thereto for effectively securing same in apredetermined relationship.

2. A transducer comprising in combination a first stack of piezoelectriccylinders spatially disposed along a first common axis, a second stackof piezoelectric cylinders partially interleaved with said first stackof piezoelectric cylinders along a second common axis, spatiallydisposed from said first common axis, means coating said first andsecond stacks of piezoelectric cylinders for electrically insulatingsame from their ambient environment, insulated means extending throughsaid coating means for timely conducting electrical energy to and fromsaid first and second stacks of piezoelectric cylinders, and meansconnected to said coating means for supporting said first and secondstacks of piezoelectric cylinders in a predetermined geometricalconfiguration.

3. A transducer comprising a plurality of stacks of axially alignedpiezoelectric convertors, each of said piezoelectric convertors of saidplurality of stacks of axially aligned piezoelectric convertors beingalternately and consecutively interleaved with the others for spatialdisposition of their respective axes a predetermined distancetherebetween, means connected to each of said axially aligned convertorsfor electrical excitation thereof as a unitary stack projector having apredetermined relative phase relationship with the other stacks, andmeans con nected to said plurality of stacks of axially alignedpiezoelectric convertors for mounting same in substantially fixedrelationship.

4. A transducer comprising in combination a first plurality of sonicenergy projectors spatially disposed along a first common axis, a secondplurality of sonic energy projectors spatially disposed along a secondcommon axis, said first and second common axes being separated from eachother by a predetermined distance whereby said first and second sonicenergy projectors are partially and alternately interleaved, meanscovering each projector of said first and second plurality of sonicprojectors for electrically insulating same from its ambientenvironment, means connected to said first and second plurality of sonicprojectors for electrically exciting same in a predetermined relativephase relationship, means connected to each projector of said pluralityof sonic projectors for securing same in substantially fixed geometricalrelationship, and means integrally connected to said projector securingmeans for mounting said transducer on a support structure.

5. A reversible electroacoustical transducer adapted to broadcast andreceive predetermined acoustical energy patterns within an aqueousmedium comprising in combination a first stack of cylindrically shapedpiezoelectric elements having diameters equal to the wavelength of theacoustical energy to be broadcast and received, said piezoelectricalelements being spatially disposed along a common axis at a distance thatis less than one-third wavelength therebetween, a second stack ofaxially aligned cylindrically shaped piezoelectric elements havingdiameters and distances therebetween equal to those of said first stackof cylindrically shaped piezoelectric elements, said first and secondstacks being interleaved in such manner that the distance between theirrespective axes may be varied as desired, electrode means respectivelyconnected to each of the piezoelectric elements of said first and secondstacks, means connected to each of said electrode means for electricallyexciting said first and second stacks as separate acoustical energyprojector units, means covering the aforesaid piezoelectric elements andelectrode means for electrically insulating same from said aqueousmedium, and means effectively connected to said last mentioned means forsecuring said first and second stacks of cylindrically shapedpiezoelectric elements in a predetermined relationship.

6. An electroacoustical transducer comprising in combination a firststack of piezoelectric elements centrically disposed along a firstcommon longitudinal axis passing therethrough, a second stack ofpiezoelectric elements similarly disposed along a second commonlongitudinal axis passing therethrough, said first and second stacks ofpiezoelectric elements being partially interleaved for predeterminedrelative spatial disposition of said first and second axes, meansrespectively interconnecting the piezoelectric elements of said firstand second stacks of piezoelectric elements for parallel electricalexcitation thereof in predetermined phase relationship, and meansconnected to each piezoelectric element of said first and second stacksof piezoelectric elements for structurally supporting same in apredetermined geometrical configuration.

7. A transducer adapted to broadcast sonic signals within an aqueousmedium upon electrical excitation and produce electrical signals uponsonic excitation received from within said aqueous medium comprising incombination, a plurality of electroacoustical converter means disposedabout a longitudinal axis, each of said electroacoustical convertermeans being partially and alternately interleaved, each of saidelectroacoustical convertor means being characterized by a predeterminedgeometrical configuration, and alternate ones of said plurality ofelectroacoustical converter means having aligned centroids disposed atdifferent positions about and parallel to the aforesaid longitudinalaxis, means coupled to each of said electroacoustical converter meansfor electrically exciting same in a predetermined relative phaserelationship when said sonic energy is being broadcast within saidaqueous medium, means connected to said electrical excitation means forvarying said relative phase relationship, and means connected to each ofsaid electroacoustical converter means for rigidily positioning same ina desired geometrical configuration.

8. A reversible transducer comprising in combination, a first pluralityof substantially identical piezoelectric cylinders. centrically disposedalong a first common axis, a second plurality of substantially identicalpiezoelectric cylinders partially interleaved with said first pluralityof substantially identical piezoelectric cylinders and centricallydisposed along a second common axis that is spatially disposed from saidfirst common axis, a pair of electrodes attached to each of thepiezoelectric cylinders of said first and second plurality ofsubstantially identical piezoelectric cylinders, conductor means coupledto each of said electrodes for connecting each of theaforesaid first andsecond plurality of substantially identical piezoelectric cylinders inelectrical parallel, means coating each cylinder of said first andsecond plurality of substantially identical piezoelectric cylinders andthe electrodes attached thereto and the aforesaid conductor means insuch manner as to insulate same from their ambient environment, and

variable inductance'and capacitor connected between said pair ofelectrical conductors, and another pair of electrical conductorsrespectively connected to the junction of said series connected variableresistor and capacitor and the junction of the aforesaid seriesconnected variable inductance and capacitance, said another pair ofelectrical conductors and one of said first mentioned electricalconductors constituting the outputs of said phase shifter which arerespectively connected to the aforesaid conductor means.

11. The device of claim 9 further characterized by an electrical signalsource connected to the input of said phase shifter.

References Cited by the Examiner UNITED STATES PATENT 2,405,604 8/46Pope.

2,416,314 2/47 Harrison 340-10 2,466,112 4/49 Keller 34010 2,508,544-5/50 Shaper.

2,697,822 1 2/54 Schuck et a1.

2,708,742 5/55 Harris 340--11 X 2,878,886 3/59 Overton.

CHESTER L. JUSTUS, Primary Examiner.

LEWIS H. MYERS, KATHLEEN H. CLAFFY, FRED- ERICK M. STRADER, Examiners.

1. A TRANSDUCER COMPRISING A PLURALITY OF STACKS OF ACOUSTICAL ENERGYPROJECTORS EACH OF WHICH IS SUCCESSIVELY AND ALTERNATELY INTERLEAVEDWITH THE OTHERS ALONG A LIKE PLURALITY OF RESPECTIVE AXES EACH OF WHICHIS SPATIALLY DISPOSED FROM THE OTHERS, MEANS CONNECTED TO EACH OF SAIDACOUSTICAL ENERGY PROJECTORS FOR TIMELY ELECTRICAL EXCITATION THEREOF,AND SUPPORT MEANS CONNECTED THERETO FOR EFFECTIVELY SECURING SAME IN APREDETERMINED RELATIONSHIP.